In most instances, a substitutive tissue must be used to recover the functionality of body tissue damaged by disease, unless the original tissues have a high inherent regeneration capacity. The unavailability of acceptable human donor organs, and the low rate of long term success thereof due to host versus graft rejection are the main challenges now facing the field of tissue and organ transplantation. In order to solve the above problems, biomaterials (such as synthetic or natural matrix serving as carriers) are provided to be implanted in the desired region to facilitate cell seeding.
According to medical statistics, approximately 30% of tissue reconstruction processes performed relates to bone tissue reconstruction. In recent years, biomaterials have been applied to reconstruct hard tissues and soft tissues of bone structures. For reconstruction of hard tissues, a key challenge is to facilitate fixation of bone fragments in an articular surface fracture or a comminuted fracture. Thus, a bone fixation device has been developed. The bone fixation device, such as a K-pin, bone nail, or cable or anchor, has a micro-textured contact surface to enhance installation or gripping characteristics thereof. For soft tissues, adherence to the bone fragments are peeled off before using bone fixation devices, thereby causing poor circulation of blood and increasing risk of nonunion fracture. In addition, when using bone fixation devices for soft tissues, bone fragments are further disintegrated following the surgical operation.
At present, most bone cements are primarily made of polymethyl methacrylate (PMMA). The bone cement can provide sufficient strength for a bone fracture at an early stage. Patients using the bone cement are not apt to develop allergies thereto due to the biologically inert properties thereof. Specifically, the bone cement is non-biodegradable. Therefore, the fixation of bone fragments using the bone cement is not a substantially complete bone union and the bone cement is not suitable for traumatic fractures. Further, other bones adjacent to the fixation of bone fragments may be broken by the bone cement due to the mechanical strength of the bone cement.
The fractures of 2-5% of patients do not heal at all, resulting in the condition known as “nonunion fracture”. Generally, bone transplantation surgeries should be used for treating nonunion fractures; especially nonunion fractures due to abnormal blood flow patterns in the bone. For treating nonunion fracture, a patient receives two surgeries, wherein one is used to collect autologous tissues from the patient and the other is used to transplant and fix the autologous tissues to the affected region. Therefore, it is necessary to develop a graft substitute in place of the autologous tissues.
Further, a bone graft substitute can be applied in the ischemic necrosis of a femoral head, such as for the reconstruction of a hip joint. Avascular necrosis (AVN) is a disease, for young adults, resulting from the temporary or permanent loss of blood supply to bones. With early diagnosis, at least 75% of the patient with AVN can recover after treatment. Various treatments for AVN focus on salvaging the head of the femur or other bones or joints may be used, such as core decompression. A necrotic tissue is first removed and packed with an autologous cancellous bone, leaving room for the insertion of an autologous fibular graft with an autologous fibular graft vascular pedicle, wherein the peroneal vessels are attached to provide abundant blood flow to the head of a femur. An anastomosis is performed between the lateral circumflex vessels and the fibula vascular pedicle. Although the procedure is oftentimes successful in stabilizing the femoral head and providing blood flow to the femoral head, it carries the risk for donor sight morbidity. A bioadhesion can be used, combined with a drug, and implanted into the femoral head. With the degradation of the bioadhesion, the drug is gradually released, facilitating the regeneration of bones and veins.
Further, bioactive substance (e.g. drugs, growth factors, nucleic acids etc.) delivery is very important for biomedical applications such as tissue engineering, cell therapy and disease medical therapy. The materials for the delivery carriers must provide biocompatible and biodegradable properties for feasible implantation. Preferably, the material is a fluid ex vivo, so that it may be easily mixed with drugs and transformed into a gel after being injected into a body by a syringe, catheter or laparoscope for delivering the bioactive substances to the desired tissue area. After, the drugs are released over time, a therapeutic effect is achieved.
Currently, few delivery materials satisfy all requirements for body compatibility. There is, therefore, still a need for a thermal sensitive and biodegradable copolymer (serving as a delivery carrier or bone graft substitute to facilitate bone healing) for treating bone diseases